Asymmetric contact lens

ABSTRACT

A contact lens comprising a corneal section, a vertical axis, and a shape adapted to maintain the lens at an intended orientation. The lens has either a visible horizontal line segment located in the corneal section perpendicular to the vertical axis and/or three visible radial line segments in the corneal section, the first of the line segments located on the vertical axis, and the second and third segments located on either side of the first segment such that the extensions of the segments would pass through a geometric center of the corneal section forming two 20° angles. The lens is useful for measuring the rotation of an asymmetric lens. Methods for measuring lens rotation using the inventive lenses are also disclosed.

BACKGROUND OF THE INVENTION

This is a Continuation-In-Part of U.S. application Ser. No. 07/203,381,filed June 7, 1988, now U.S. Pat. No. 4,976,533.

Astigmatism is a defect in the eye that is corrected by a lens with anasymmetric prescription. The asymmetric prescription, which is usuallyexpressed as cylinder on the patient's prescription order, causes atleast a portion of the surface of the lens to have the shape of a toricsegment. Hence, such lenses are called toric lenses. The asymmetricprescription must be correctly oriented with respect to the eye of thewearer. For ordinary eyeglasses, this presents no problem, because thelens is permanently fixed to the frame at the correct orientation, andthe frame is non-rotatably attached to the wearer's face by theearpieces and nosepiece. For a toric contact lens, orientation is not sosimple.

One method of maintaining correct orientation of the lens is toconstruct the lens with its intended bottom third thicker than itsintended top two thirds. The blinking of the patient's eyelid tends topush the thicker intended bottom of the lens to the bottom of the eye.However, because of irregularities in the shape of the cornea,interference by the lower lid, etc., the intended bottom of the lensdoes not always settle at the exact bottom of the eye. Another way tomaintain lens orientation is to construct the lens with a relativelythick central zone and thinner top and bottom zones. However, lenses ofthis type are also capable of settling to a position that is differentfrom that intended. Very often a lens of either type settles to aposition that is rotated 5 or more degrees from its intended position.This rotation must be measured and taken into account in the cylinderportion of the lens prescription.

DESCRIPTION OF THE DRAWINGS

Prior art methods of measuring lens rotation and the inventive methodsare best described with reference with the accompanying drawingswherein:

FIG. 1 illustrates a prior method of measuring rotation wherein the lenshas a small evacuated circle (i.e. a dimple) at its intended bottom.

FIG. 2 illustrates another prior method wherein the lens has radial linesegments at 30° angles to each other.

FIG. 3 illustrates yet another prior method wherein the lens has twohorizontal bars on its "equator".

FIG. 4 illustrates still another prior method wherein the lens has abottom truncation, i.e. its lower portion is removed.

FIG. 5 illustrates an embodiment of the present invention wherein thelens has a horizontal line segment located between its center andbottom.

FIG. 6 illustrates another embodiment of the present invention whereinthe lens has radial line segments at 20° angles to each other.

FIG. 7 illustrates a preferred embodiment of the present inventionwherein the features of FIGS. 5 and 6 are combined.

FIG. 8 illustrates schematically a cross-section of the lenses of FIGS.1, 2, and 5 to 7 showing that these lenses are thicker at the bottomthan at the top.

FIG. 9 illustrates a cross section of the lens of FIG. 3 showing itsrelatively thick central zone and thinner top and bottom zones.

FIG. 10 illustrates schematically a cross section of the lens of FIG. 4showing that it is thicker at the bottom than at the top.

FIG. 11 illustrates the dimensions of the line segments in accordancewith the invention.

FIGS. 12 to 21 illustrates alternative embodiments of the presentinvention.

DESCRIPTION OF THE PRIOR ART

All of the lenses illustrated in FIGS. 1 to 4 (prior art) and 5 to 7(the present inventions) are shaped to maintain a fixed rotationalorientation when worn. The prior art lenses of FIGS. 1 and 2, and theinventive lenses of FIGS. 5 to 7 have cross sections as shown in FIG. 8.The lower third of these lenses is thicker than the top two thirds.Blinking of the wearer's upper lid pushes bottom 100 downward, whilekeeping top 101 near the top of the eye. The prior art lens of FIG. 3 isshown in cross section in FIG. 9. The center section 102 of this lens isthicker than the top 101" and bottom 100". The thicker zone of the lensof FIG. 3 is located between the dotted lines in FIG. 3. FIG. 10 is across-sectional view of the prior art lens of FIG. 4. This cross sectionis the same as FIG. 8, except that a small portion of the lens bottom,shown dotted, has been removed.

The exact shaping of the inventive lenses is not a part of thisinvention. Although the cross section of FIG. 8 is preferred, anyequivalent shaping intended to maintain rotational orientation willsuffice.

In FIG. 1, lens 10 has a small visible circle 11 located at its intendedbottom. The circle is drilled part way through the lens and is easy tosee in the bright light of a slit lamp. To measure rotation of the lensof FIG. 1, the eyecare practitioner places a trial lens on the eye ofthe wearer and, with a slit lamp, projects a narrow beam of light acrossthe center 12 of the patient's pupil 13 and dot 11. The angle formed bythe narrow light beam and the vertical 17 is considered to be therotation of the lens. However, this method of measuring rotation hasseveral disadvantages:

1) The beam of the slit lamp must pass through the center of the pupilinto the eye of the patient. Most patients find this very uncomfortablesince it can be equivalent to looking into the continuous flash of acamera for 10 to 15 seconds.

2) Not all pupils are centered within the cornea. In FIG. 1 the center12 of pupil 13 is shown located to the right of the geometrical center16 of cornea 14. In anatomical terms the pupil's center 12 is said to belocated nasally (i.e. toward axis N, of nose N) from the cornea'sgeometrical center 16. Furthermore, most often a contact lens settles toa position wherein its center is not located on the geometrical centerof the cornea. Instead, the lens' center settles to a position that isover the apex of the cornea. In FIG. 1, the center 15 of lens 10 islocated to the left of the geometric center 16 of cornea 14. Inanatomical terms the lens' center and corneal apex 15 is said to belocated temporally (i.e. away for axis N' of nose N) from the cornea'sgeometrical center 16. This is the usual centering position of both softand hard contact lenses. Such off-center locations can cause errors inthe measurement of lens rotation. In FIG. 1, the angle formed by theslit-lamp beam passing through the center 12 of the pupil and smallcircle 11 and the vertical 17 is angle A. Using the lens of FIG. 1 tomeasure rotation would cause the practitioner to use the angle A as theamount of lens rotation. However, the angle formed by a line passingthrough the true center 15 of the lens and circle 11 and the vertical 17is only angle B. Hence use of the method of FIG. 1 would cause thepractitioner to use angle A as the amount of rotation when angle B isthe actual rotation. It is believed that errors of up to about 15° canoccur when using the lens of FIG. 1.

3) The prior art lenses of FIG. 1 are hydrophilic lenses, which arelarger than the cornea, and small circle 11 is located below cornea 14under the normal position L of the lower eyelid as show in FIG. 1. Whenthe lens is on the patient's eye, the circle is covered by the lower lidand the practitioner must pull the lower lid away when making themeasurement. This can cause the lens to rotate from its normal positionwith the lower lid in place.

4) If the practitioner does not have a slit lamp, there is no way toestimate the rotation with any kind of accuracy.

5) Deposits of protein can accumulate in small circle 11.

6) Although small circle 11 is easy for the practitioner to see with thebenefit of a slit lamp, it is difficult for the patient to see wheninserting the lenses in normal lighting. Hence the patient might insertthe lens upside-down or sideways. A lens so inserted might not assumeits intended orientation despite its shaping.

A second prior method for measuring lens rotation is shown in FIG. 2.Here lens 10A has three line segments 20, 21 and 22, the extensions ofwhich would pass through center 15 of the lens. Segments 20, 21 and 22are located such that the angles C and C' formed by the extensions ofsegments 20 and 21 and of segments 21 and 22 are 30°. The line segmentsare etched into the lens with a laser.

To measure rotation with the lens of FIG. 2, the practitioner uses aslit lamp to form a narrow beam of light from the center of pupil 13 tomiddle segment 21. The angle formed by this beam and the vertical isused as the amount of rotation. Alternatively, if the practitioner doesnot have a slit lamp, the practitioner can estimate the amount ofrotation based on his knowledge that the segment are 30° apart.

However, practice of the method of FIG. 2 has several disadvantages:

1) The slit lamp beam must pass through the pupil, causing discomfort,as with the method of FIG. 1.

2) Decentralization of the pupil with respect to the center of thecornea, or of the lens with respect to the center of the cornea, or bothcan cause the measurement to be inaccurate as with the method of FIG. 1.

3) The line segments are located below the cornea 14, under the normalposition L of the lower lid, so that it is necessary to pull away thelower lid when making the measurement. This can also cause inaccuracy aswith the method of FIG. 1.

4) When estimating the rotation without a slit lamp, it is easy toestimate rotation of 15° or 30°, but difficult to estimate rotations of5°, 10°, 20° or 25°. That is, the 30° spacing of the line segments isnot optimum.

5) Deposits can accumulate on the etched lines 20, 21 and 22.

6) The etched lines are difficult for the patient to see, which cancause upside-down or sideways insertion, as with the lens of FIG. 1.

FIG. 3 illustrates a third prior method for measuring rotation. Lens 10Bof FIG. 3 has two horizontal line segments 31 and 32 located on ahorizontal equator 33 of the lens. Line segments 31 and are very lightlyetched onto the lens.

To measure rotation with the lens of FIG. 3, the practitioner focusesthe beam of a slit lamp along line segments 31 and 32. The beam alsoenters the patient's eye through pupil (13). The angle formed by thebeam and the horizontal is the amount of lens rotation.

The method of FIG. 3 has several disadvantages:

1) The slit lamp beam must pass through the as with the method using thelens of FIG. 1.

2) Because segments 31 and 32 are lightly etched, they are verydifficult to see, even with a slit lamp.

3) There is no way to accurately estimate rotation when a slit lamp isunavailable.

4) Deposits may accumulate on the etched line segments.

5) The lens may flex when on the eye causing line segments 31 and 32 tomove off the equator of the lens. Such flexing can give a falsemeasurement of the lens's rotation.

6) It is difficult for the wearer to tell the bottom from the top of thelens, possibly causing upside-down or sideways placement on the eye.

FIG. 4 shows a fourth prior method for measuring lens rotation. Here,the lens 10C is truncated so that it has a flat, or nearly flat bottom40.

To practice the method of FIG. 4., the practitioner focuses a slit lampbeam along truncation 40. The angle formed by the beam and thehorizontal is the amount of rotation.

This method also has some disadvantages:

1) The lower lid L has to be pulled away to make the measurement, whichcan cause the rotation to change from its normal position with the lowerlid in place, as with the lens of FIG. 1.

2) This is no way to estimate rotation without a slit lamp.

3) Truncated lenses are perceived to be uncomfortable by many patients.

SUMMARY OF THE INVENTION

A first aspect of the invention may be summarized as follows:

a contact lens comprising:

A. a cornea section intended to cover the cornea of the wearer;

B. a vertical axis having a top intended to be located at the top of thewearer's eye and bottom intended to be located at the bottom of thewearer's eye;

C. a shape adapted to maintain said lens at its intended orientationwithin the eye;

D. a visible horizontal line segment located within said corneal sectionperpendicular to said vertical axis; and

E. an asymmetric prescription located over at least a portion of saidcorneal section.

In a second aspect of the invention the lens has three visible radialline segments located in said corneal section, the first of said radialline segments located on said vertical axis and the second and third ofsaid radial line segments located on either side of said first radialline segment, said radial line segments located such that theirextensions would pass through a geometrical center of said corneasection forming two 20° angles.

In a third aspect of the invention the lens has:

(a) a visible horizontal line segment located within said cornealsection, perpendicular to said vertical axis; and

(b) three visible radial line segments located in said corneal section,the radial line segments or their extensions intersecting said visiblehorizontal line segment or its extensions, the first of said radial linesegments located on said vertical axis and the second and third of saidradial line segments located on either side of said first radial linesegment, said radial line segments located such that their extensionswould pass through a geometrical center of said corneal section forming20° angles.

In preferred embodiments of the invention the line segments arepigmented and/or the lens is a hydrophilic lens further comprising ascleral section surrounding the corneal section and/or the lens furthercomprises an asymmetric prescription located over at least a position ofsaid corneal section. The pigmented lines make it very easy for thepatient to distinguish the bottom of the lens from the top, therebysubstantially eliminating upside-down insertion.

The invention also comprises methods for measuring rotation using theinventive lenses.

DETAILED DESCRIPTION OF THE INVENTION

A first aspect of the present invention is illustrated in FIG. 5. Lens50 has the usual elements of conventional asymmetric contact lenses. Acorneal section 14, is intended to cover the wearer's cornea when thelens is worn. Within corneal section 14, there is a pupil sectionintended to cover the patient's pupil 13. If the lens is hydrophilic, itwill have an outer or scleral section 51 surrounding corneal section 14,An imaginary vertical axis 17 has a top 17, which is intended to belocated at the top of the wearer's eye and a bottom 17" intended to belocated at the bottom of the wearer's eye. The lens has a shape adaptedto maintain the lens at its intended orientation. Preferably the bottomof the lens is relatively thicker than the top, as shown schematicallyin FIG. 8 to maintain the lens at its intended orientation, i.e. withthe top 17, of axis 17 at the top of the eye and the bottom 17" of axis17 at the bottom of the eye. Of course other shapes adapted to maintainthe lens at its intended orientation, such as those illustrated in FIGS.3 and 9, and FIGS. 4 and 10 may also be used.

In order to measure the rotation of lens 50 when it is on the eye of theintended wearer, visible horizontal line segment 52 is provided. Therotation of the lens is the angle formed between vertical axis 17 andthe true vertical axis of the wearer's eye, not shown. When thepractitioner measures rotation using the lens of FIG. 5, as describedlater, he actually measures the angle formed by line segment 52 and thetrue horizontal, which is the same as the rotation described in theprevious sentence. Line segment 52 is located within corneal section14', perpendicular to vertical axis 17 such that line segment 52 and itsextensions are outside of the lens's pupil section. Preferably segment52 is below the patient's pupil 13, as shown in the drawing.

For greater visibility it is preferred that line segment 52 bepigmented, i.e. be formed of an ink, paint, or other material containingpigment. Methods for depositing a pigmented marking on the surface of alens are disclosed in Loshaek's U.S. Pat. No. 4,668,240. Briefly, in apreferred method, a contact lens constructed of polymer havingfunctional groups selected from at least one of --COOH, --OH AND--NH--R, wherein R is hydrogen or C₁ to C₈ alkyl is provided.Conventional hydrophilic lenses constructed at least partially ofpoly(hydroxyethyl methacrylate), which have the functional groups --OH,may, for example, be used. An ink comprising pigment, binding polymerhaving functional groups selected from --COOH, --OH or --NH--R and anadditional compound having at least two groups per molecule of --NCO orepoxy, is prepared. Horizontal line 52 is stamped on the lens using theink and the ink is cured, e.g. by heat. Of course, other methods ofplacing line segment 52 on the lens are possible, e.g. by cutting theline segment into the lens with a laser or by lightly abrasive etching.However, such cut lines are not as easy to see as pigmented lines.Furthermore, cut or etched line segments have the potential to attractdeposits; hence pigmented line segments are highly preferred. Inaddition to line segment 52, this paragraph applies to all other visibleline segments of this invention.

To use the lens of FIG. 5 for measuring rotation, the practitionerdisposes the lens on the eye of the patient and, with the patient's headin a vertical position, projects a narrow beam of light onto segment 52.The angle formed by the light beam and the true horizontal of thepatient's eye is the amount of rotation of the lens.

After the measurement is taken, a lens having the same diameter and rearcurve as lens 52 is provided and the patient's asymmetric prescriptionis lathe cut, molded, or spun cast into the lens, taking into accountthe amount of rotation. This new lens also has segment 52 on it so that:

(1) The practitioner can measure the rotation of the new lens on thepatient's eye, and

(2) The patient can use segment 52 to avoid inserting the lens upsidedown or sideways. This is desirable because a lens inserted upside downor sideways might not right itself, resulting in less than optimumvision.

A more accurate measurement of the rotation of the lens actuallyprescribed for the patient can be achieved, if the lens used toinitially measure rotation contains a prescription that is approximatelyequal to that of the patient's prescription. Hence, the lens used toinitially measure rotation will preferably have an asymmetricprescription located over at least a portion of its corneal section. Ofcourse, the lens that is finally dispensed to the patient also has sucha prescription.

Use of the lens of FIG. 5 to measure rotation has several advantagesover use of prior art lenses:

1. Patient discomfort is avoided because the slit lamp does not have topass through the patient's pupil. Use of the prior art lenses of FIGS.1, 2 and 3 does not have this advantage.

2. The pupil's center is not used as a reference point. Hence, theinaccuracies possible when using the lenses of FIGS. 1 and 2 areavoided.

3. The lower lid of the patient's eye does not have to be pulled away tomeasure the rotation. Hence, the inaccuracies possible when using thelenses of FIGS. 1, 2 and 4 are avoided.

4. If line segment 52 is pigmented, there will be no depressions in thelens to collect deposits, as with the lenses of FIGS. 1 to 3.

5. If line segment 52 is pigmented, it will be easier to see than theetched or drilled indicia of FIGS. 1 to 3.

6. There need be no truncation perceived to be uncomfortable by many.

7. Lens flexure effects will not affect the measurement accuracy, aswith the lens of FIG. 3.

A second aspect of the invention is illustrated in FIG. 6. The lens 60has the usual aspects of prior art lenses, i.e. corneal section 14',vertical axis 17, and a shape intended to maintain the lens'sorientation. As with prior art methods, the lens may have an asymmetricprescription over at least the patient's pupil 13.

For measuring rotation, the lens has three visible radial line segments61, 62 and 63 located in corneal section 14'. Line segments 61, 62 and63 are preferably pigmented. A first radial line segment 62 is locatedon vertical axis 17. Second and third radial line segments 61 and 63 arelocated on either side of first line segment 62 such that theirextensions, shown dotted, would pass through geometrical center 15' ofcorneal section 14' forming two 20° angles D and E.

To use the lens of FIG. 6 to measure rotation, the practitioner focusesa slit lamp beam over segment 62 and the center 15' of the pupil 13 anduses the angle formed by the beam and the true vertical as the measureof rotation. Using the lens of FIG. 6 to measure rotation has some ofthe disadvantage of using the lens of FIG. 2 in that the slit lamp'sbeam must pass through the patient's pupil and decentralization of thepupil or lens can introduce inaccuracies. However, the potentialinaccuracy introduced by pulling the lower lid away is avoided becausethe line segments are located on the corneal section of the lens.Furthermore, use of pigmented line segments renders them easier to see.

Without a slit lamp, the practitioner may use his knowledge that thesegments are 20° apart to estimate the rotation. Use of the lens of FIG.6 to estimate rotation without slit lamp has advantages over use of thelens of FIG. 2 in that:

(a) the lower lid need not be pulled away to see the line segments, and

(b) the 20° spacing of the radial line segments makes it very easy toestimate rotations of 5°, 10°, 15° and 20°, and by extrapolation,rotations of 25° and 30°.

The preferred embodiment of the inVention is illustrated in FIG. 7. Lens70 has the same conventional features as the lenses of FIGS. 5 and 6,i.e., corneal section 14', vertical axis 17, shape for maintainingorientation, and an optional asymmetric prescription over at least thepatient's pupil 13.

For measuring rotation lens 70 has a combination of the features oflenses 50 and 60 of FIGS. 5 and 6 respectively. A visible, preferablypigmented, horizontal line segment 52 is located within corneal section14', perpendicular to vertical axis 17. Three visible, preferablypigmented, radial line segments 61, 62 and 63 are also located in thecorneal section. Radial line segments 61, 62 and 63 or their extensionsintersect horizontal segment 52. In the embodiment of FIG. 7, radialsegments 61, 62 and 63 terminate at horizontal segment 52. First radialsegment 62 is located on vertical axis 17, and second and third radialsegments 61 and 63 are located on either side of first segment 62.Extensions of line segments 61, 62 and 63, shown dotted, would passthrough the geometrical center 15 of corneal section 14' forming two 20°angles D and E.

To use the lens of FIG. 7 for measuring rotation, the practitionerprojects a narrow beam of light from a slit lamp across horizontalsegment 52 and uses the angle formed by the narrow beam and the truehorizontal as the measure of rotation. This method of measuring rotationhas all the advantages of use of the lens of FIG. 5. To measure rotationwithout a slit lamp, the practitioner compares positions of radial linesegments 61, 62 and 63 with the true vertical. This method has all ofthe advantages of using the radial line segments of FIG. 6 for measuringrotation without a slit lamp.

FIG. 11 illustrates the preferred dimensions for visible line segmentsin accordance with the invention, which are as follows:

90--length of horizontal line segment, preferably from 1.5 to 5 mm, morepreferably about 4.5 mm;

91--length of center radial line segment, preferably from 0.5 to 3.5 mm,more preferably about 1.4 mm;

92--length of outside radial line segments, preferably from 0.3 to 3.0mm, more preferably about 1 mm;

93--distance from geometric center of lens 15' to horizontal linesegment, preferably from 0 to 6 mm, more preferably from 3.5 to 6 mm,and most preferably about 4.2 mm.

94--thickness of all line segments, if pigmented, preferably about 0.01to 1.0 mm, more preferably about 0.3 mm. If the more preferred thicknessis used, the line segments will be easy for the practitioner and patientto see at close distances, but not easy to see at ordinary viewingdistances when the lens is worn. For hydrophilic lenses, thesemeasurements apply to the lens in the hydrated state.

Distance 93 will normally be greater than zero. However, even if thehorizontal line segment is on geometric center 15', i.e., even ifdistance 93 is zero, the lens still can be used for measuring rotationin test lenses.

In a preferred embodiment the above dimensions are used, but the linesegments are dotted, as shown in FIGS. 19, 20, and 21.

FIGS. 12 to 17 illustrate some alternative embodiments of the inventionof FIG. 7. In FIG. 12 the horizontal segment does not extend beyond theradial line segments.

In FIG. 13 the radial line segments cross the horizontal line segment,which does not extend beyond the radial line segments.

In FIG. 14 the radial line segments cross the horizontal line segment,which extends beyond the radial line segments.

In FIG. 15, only the extension (shown dotted) of the radial linesegments intersect the horizontal line segment.

In FIG. 16 the center radial segment crosses the horizontal segment,while only the extensions of the outer line segments intersect thehorizontal segment.

In FIG. 17 only the extensions of the horizontal line segment intersectonly the extensions of the outer radial segments. The center radialsegment crosses the horizontal segment.

In FIG. 18 one of the outside radial line segments, i.e., one of thesegments that is not located on the vertical axis, is shorter than theother outside line segment. This allows the patient to determine whenthe lens has been inadvertantly turned inside out. For example, if thepatient knows that the short line segment belongs on the right hand sideof the lens, if the short segment is on the left hand side, the patientwill know that the lens is inside out.

In general, any lens marking that is asymmetric about the vertical axismay be used to determine whether a lens is inside out. Use of asymmetricmarkings has been disclosed in U.S. Pat. No. 4,525,044 (Bauman), but notin combination with the lens markings of this invention.

FIG. 19 illustrates an alternative embodiment of the invention whereinhorizontal line segment 52' is formed by a series of dots arranged in ahorizontal line. Line segments 61', 62', and 63' are also formed bydots. Extra marking, dots 190, fill the angle formed by line segments61' and 52' so that the marking, as a whole is asymmetric about thevertical axis.

FIG. 20 illustrates yet another alternative embodiment of the invention.Here the mark on the lens has a horizontal line segment 52", formed ofdots, and additional marking 200 in the form of a slanted line segmentto cause the mark to be asymmetric about the vertical axis.

FIG. 21 illustrates still another alternative embodiment of theinvention wherein horizontal line segment 52", formed of dots, hasadditional marking 210 in the form of extra dots to cause the mark to beasymmetric about the vertical axis.

Of course other alternative embodiments in accordance with the appendedclaims are operable.

It can be seen that the present invention provides a method and lensesfor measuring the rotation of a lens that, in its preferred embodiments,overcomes all of the disadvantages of the prior art.

What is claimed is:
 1. A contact lens comprising: p1 A. a cornealsection intended to cover the cornea of the wearer;B. a pupil sectionwithin said corneal section intended to cover the pupil of the wearer;C. a vertical axis having a top intended to be located at the top of thewearer's eye and bottom intended to be located at the bottom of thewearer's eye; D. a shape adapted to maintain said lens at its intendedorientation within the eye; E. a visible horizontal line segment locatedwithin said corneal section perpendicular to said vertical axis, saidline segment and its extensions being outside of said pupil section; F.an asymmetric prescription located over at least a portion of saidcorneal section, and G. extra marking to cause the combination of saidline segment and extra marking to be asymmetric about said verticalaxis.
 2. The lens of claim 1 wherein said line segments are formed ofdots.
 3. A contact lens comprising:A. a corneal section intended tocover the cornea of the wearer; B. a vertical axis having a top intendedto be located at the top of the wearer's eye and bottom intended to belocated at the bottom of the wearer's eye; C. a shape adapted tomaintain said lens at its intended orientation within the eye; D. avisible horizontal line segment located within said corneal sectionperpendicular to said vertical axis; E. three visible radial linesegments located in said corneal section, the radial line segments ortheir extensions intersecting said visible horizontal line segment orits extensions, the first of said radial line segments located on saidvertical axis and the second and third of said radial line segmentslocated on either side of said first radial line segment, said radialline segments located such that their extensions would pass through ageometrical center of said corneal section forming 20° angles, and F.extra marking to cause the combination of said horizontal line segment,said radial line segments and said extra marking to be asymmetric aboutthe verticle axis.
 4. The lens of claim 2 wherein said extra marking islocated within an angle formed by an intersection of said horizontalline segment and one of said line segments located on a side of saidvertical axis.
 5. The lens of claim 3 wherein said line segments areformed of dots.
 6. The lens of claim 4 wherein said line segments areformed of dots.